The broad, long-term objectives of this proposal are to better understand the role of alcohol in aviation and motor carrier accidents and to improve transportation safety. The specific aims are: (1) to determine the point prevalence rates of alcohol violations among safety-sensitive employees in aviation and motor carriers;(2) to quantify the relative risks of aviation and motor carrier accidents associated with alcohol violations;(3) to examine the deterrent effects of mandatory alcohol testing programs on alcohol violations in aviation employees and commercial truck drivers;and (4) to evaluate the effectivenessof mandatory alcohol testing programs in reducing aviation and motor carrier accidents. The Omnibus Transportation Employee Testing Act of 1991 mandates that employees with safety- sensitive functions be tested for alcohol under a variety of circumstances. Mandatory alcohol testing programs such as random testing, reasonable suspicion testing, and post-accident testing have been implemented in the aviation and motor carrier industries since 1995 but have not been rigorously evaluated. This application is a competing continuation to an R01 grant on alcohol and general aviation (i.e., noncommercial flights). In the parent project, the investigators followed a cohort of 335,672 general aviation pilots for seven years and found that driving-while-intoxicated history is a valid risk marker for flight safety and that alcohol plays a particularly important role in crashes involving flight under visual flight rules into instrument meteorological conditions. In the proposed project, the investigators will address the specific aims through a series of case-control studies and time series analyses using alcohol testing data (for the years 1995-2007) and accident and exposure data (for the years 1983-2007) from a variety of surveillance systems maintained by federal agencies, including the Federal Aviation Administration, Federal Motor Carrier Safety Administration, National Transportation Safety Board, National Highway Traffic Safety Administration, and Bureau of Transportation Statistics. The proposedproject will help address several national health objectives pertaining to alcohol abuse, injury control, occupational safety, andintervention effectiveness research, as statedin Healthy People 2010. Findings from theproposed research couldprovide much-neededscientific evidence for informing important policy decisions relevant to transportation safety andprotection of the traveling public.